This invention relates to thermal heads capable of reading and/or writing optical images, and more particularly to a thermal head in which a reading section is coupled to a writing section through a thin film transistor, so that, even when the reading section produces a very small level signal, an output large enough to drive the writing section can be provided by switching the coupling transistor.
In many output devices utilizing conventional thermal heads, a reading device and a thermal printing head, which is a recording device, are separately arranged, and video signals are transmitted and received spatially separately.
Sometimes, a facsimile device capable of transmitting and receiving video signals is employed as a copying machine.
However, in many cases, two devices, namely, a reading device and a reproducing device must be provided, which not only increases the manufacturing cost but also results in an uneconomical waste of space. This drawback may be eliminated by forming the thermal head and a picture reading photo-sensitive element into one unit. However, this method causes another problem in that the service life is decreased, because the photo-sensitive element is greatly deteriorated by generated heat.
In order to overcome these difficulties, a device has been disclosed by Japanese Patent Application No. 37033/1979 in which a signal from a reading device is used directly as a current in the thermal head output device. Therefore, the head itself must be a photo-conductor which can supply current sufficiently, which limits kinds of materials which can be used for manufacturing the device. Thus, the conventional device is not practical.
The conventional device suffers from another problem in that the light receiving element is deteriorated by the heat generated because a large current for driving the heat-sensitive head flows in the light receiving element.